| |
| |
| 8.
Direct Brain–Computer Communication |
| |
8.2.
Neurophysiological considerations
| |
8.2.1.
Dynamics of Brain Oscillations |
|
Two types of oscillations have importance
for the BCI:
| |
1)
the Rolandic mu rhythm in the range 7–13
Hz |
| |
2)
the central beta rhythm above 13 Hz. |
Both rhythms originate in the sensorimotor cortex.
Sensory stimulation, motor behavior, and mental imagery can
change the functional connectivity within the cortex and results
in:
| |
1)
an amplitude suppression [event-related
desynchronization (ERD)] of mu and central beta rhythms. |
| |
2)
an amplitude enhancement [event-related
synchronization (ERS)] of mu and central beta rhythms. |
Preparation and planning of self-paced
hand movement results in a short-lasting desynchronization (ERD)
of Rolandic mu and central beta rhythms. In other words Beta
oscillations desynchronized during the preparation and execution
of a motor act.
However, alpha and beta frequency components differ with respect
to temporal behavior.
The picture (upper panel) presents
data from a voluntary movement experiment demonstrating the existence
of at least three different types of oscillations at the same
electrode location over the sensorimotor hand area during brisk
finger lifting.
The alpha band (mu) ERD (10–12 Hz) starts 2.5 s before movement-onset,
reaches maximal desynchronization shortly after movement-onset,
and recovers to baseline level within a few seconds. The central
beta activity (14–18 Hz), in contrast, displays a short-lasting
ERD during initiation of movement followed by a synchronization
(ERS) with a maximum after movement execution.
 |
Picture:
Upper panel: Superimposed band power time courses computed
for three different frequency bands (10–12 Hz, 14–18
Hz, and 36–40 Hz) from EEG trials recorded from
electrode position C3 during right index finger lifting.
EEG data are triggered with respect to movement-offset
(vertical line at t = 0 s). Note the beginning of mu ERD
around 2.5 s prior to movement-offset, the maximum of
gamma ERS immediately prior to movement-onset and the
maximum of the beta ERS within the first second after
movement-offset. Lower panel: Examples of ongoing EEG
recorded during right finger movement. Movement-onset
at t = 0 s. Note the EEG desynchronization (ERD) at central
electrode locations prior to movement-onset and the enhanced
alpha band activity over the posterior region (ERS) during
movement. |
Source:
Motor Imagery and Direct Brain–Computer Communication, Gert Pfurtscheller and Christa Neuper |
|
|
